TS4975

Application Information

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Output capacitor Cout

In single-ended mode the external output coupling capacitors Cout are needed. This coupling

capacitor Cout with the output load RL also forms a first-order high-pass filter with -3 dB cut off

frequency.

These two first-order filters form a second-order high-pass filter. The -3 dB cut-off frequency of

these two filters should be the same, so the following formula should be respected:

4.4

Decoupling of the circuit

Two capacitors are needed to properly bypass the TS4975 — a power supply capacitor Cs and

a bias voltage bypass capacitor Cb.

Cs has a strong influence on the THD+N in high frequency (above 7kHz) and indirectly on the

power supply disturbances.

With 1

µF, you could expect similar THD+N performances like shown in the datasheet.

If Cs is lower than 1

µF, THD+N increases in high frequency and disturbances on power supply

rail are less filtered.

To the contrary, if Cs is higher than 1

µF, those disturbances an the power supply rail are more

filtered.

Cb has an influence on THD+N in lower frequency, but its value is critical on the final result of

PSRR with input grounded in lower frequency:

●

If Cb is lower than 1

µF, THD+N increases at lower frequencies and the PSRR worsens

upwards.

●

If Cb is higher than 1

µF, the benefit on THD+N and PSRR in the lower frequency range is

small.

The value of Cb also has an influence on startup time.

4.5

Power-on reset

When power is applied to Vdd, an internal Power On Reset holds the TS4975 in a reset state

until the supply voltage reaches its nominal value.

The Power On Reset has a typical threshold of 1.75V.

F

CL

1

2

πR

-------------------------- Hz

()

=

1

2

πZ

------------------------

1

2

πR

--------------------------

≅